After removing the drain cover, I discovered a white cap screwed into the side of an apparent insert of some type, After removing the white cap, do I need to remove this (insert?) in order to use EEL to unclog this sewer drain? If so, then how?

After removing the drain cover, I discovered a white cap screwed into the side of an apparent insert of some type, After removing the white cap, do I need to remove this (insert?) in order to use EEL to unclog this sewer drain? If so, then how?
This white cap is the floor drain clean out, (see image) this bypases the trap and gives your snake a straight shot at the clog. Remove the insert and send your snake down the opening. Good luck, Tom

Speedball, we rented a 4" auger, as suggested by the rental folks, it does not seem to fit through the opening after removing white cap, would the 2" auger have been a better idea?

They suggested a 4" auger for a 1 1/2 " cleanout opening on a floor drain? Go back and tell them you wish to rent a Ridged K-30 sink machine, or equivalent, with a small auger tip. Or you could purchase a hand held power snake,(see image) and have the tool handy for the next clog.

S.B.

I'm sorry to keep bothering you, I told them it was a floor drain to the sewage (which it is) it occasionally gets roots into the line and that's why it clogs, we have had plumbers out in the past and they used "something" like what I rented. I don't believe a "snake" would be strong enough to break up these roots, am I wrong?

I don't believe a "snake" would be strong enough to break up these roots, am I wrong?You shouldn't be bothered with roots in a floor drain. But if you have roots a snake will auger into it and pull them back. You're not going to get a cutter tip through the floor drain clean out. Use the auger to clear the line and if roots are a problem then let's control them. For immediate relief and to kill the existing roots and prevent further growth you can purchase RootX or Robics Foaming Root Killer that contain Dichlobrnic.
A less expensive way would be to call around to garden supply stores and ask for fine grain Copper Sulphate. Put a 1/2 pound in your toilet and flush it down. Repeat in 6 months. Good luck, tom